bpf: XDP metadata RX kfuncs

Define a new kfunc set (xdp_metadata_kfunc_ids) which implements all possible
XDP metatada kfuncs. Not all devices have to implement them. If kfunc is not
supported by the target device, the default implementation is called instead.
The verifier, at load time, replaces a call to the generic kfunc with a call
to the per-device one. Per-device kfunc pointers are stored in separate
struct xdp_metadata_ops.

Cc: John Fastabend <john.fastabend@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Anatoly Burakov <anatoly.burakov@intel.com>
Cc: Alexander Lobakin <alexandr.lobakin@intel.com>
Cc: Magnus Karlsson <magnus.karlsson@gmail.com>
Cc: Maryam Tahhan <mtahhan@redhat.com>
Cc: xdp-hints@xdp-project.net
Cc: netdev@vger.kernel.org
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20230119221536.3349901-8-sdf@google.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

3 files changed, 76 insertions, 1 deletions

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 1cf19da3c128..16da51093aff 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2096,6 +2096,14 @@ bool bpf_prog_map_compatible(struct bpf_map *map,
 	if (fp->kprobe_override)
 		return false;
 
+	/* XDP programs inserted into maps are not guaranteed to run on
+	 * a particular netdev (and can run outside driver context entirely
+	 * in the case of devmap and cpumap). Until device checks
+	 * are implemented, prohibit adding dev-bound programs to program maps.
+	 */
+	if (bpf_prog_is_dev_bound(fp->aux))
+		return false;
+
 	spin_lock(&map->owner.lock);
 	if (!map->owner.type) {
 		/* There's no owner yet where we could check for
diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c
index f767455ed732..3e173c694bbb 100644
--- a/kernel/bpf/offload.c
+++ b/kernel/bpf/offload.c
@@ -755,6 +755,50 @@ void bpf_dev_bound_netdev_unregister(struct net_device *dev)
 	up_write(&bpf_devs_lock);
 }
 
+int bpf_dev_bound_kfunc_check(struct bpf_verifier_log *log,
+			      struct bpf_prog_aux *prog_aux)
+{
+	if (!bpf_prog_is_dev_bound(prog_aux)) {
+		bpf_log(log, "metadata kfuncs require device-bound program\n");
+		return -EINVAL;
+	}
+
+	if (bpf_prog_is_offloaded(prog_aux)) {
+		bpf_log(log, "metadata kfuncs can't be offloaded\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+void *bpf_dev_bound_resolve_kfunc(struct bpf_prog *prog, u32 func_id)
+{
+	const struct xdp_metadata_ops *ops;
+	void *p = NULL;
+
+	/* We don't hold bpf_devs_lock while resolving several
+	 * kfuncs and can race with the unregister_netdevice().
+	 * We rely on bpf_dev_bound_match() check at attach
+	 * to render this program unusable.
+	 */
+	down_read(&bpf_devs_lock);
+	if (!prog->aux->offload)
+		goto out;
+
+	ops = prog->aux->offload->netdev->xdp_metadata_ops;
+	if (!ops)
+		goto out;
+
+	if (func_id == bpf_xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_TIMESTAMP))
+		p = ops->xmo_rx_timestamp;
+	else if (func_id == bpf_xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_HASH))
+		p = ops->xmo_rx_hash;
+out:
+	up_read(&bpf_devs_lock);
+
+	return p;
+}
+
 static int __init bpf_offload_init(void)
 {
 	return rhashtable_init(&offdevs, &offdevs_params);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index bba68eefb4b2..9009395206f8 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2333,6 +2333,12 @@ static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, s16 offset)
 		return -EINVAL;
 	}
 
+	if (bpf_dev_bound_kfunc_id(func_id)) {
+		err = bpf_dev_bound_kfunc_check(&env->log, prog_aux);
+		if (err)
+			return err;
+	}
+
 	desc = &tab->descs[tab->nr_descs++];
 	desc->func_id = func_id;
 	desc->imm = call_imm;
@@ -15772,12 +15778,25 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 			    struct bpf_insn *insn_buf, int insn_idx, int *cnt)
 {
 	const struct bpf_kfunc_desc *desc;
+	void *xdp_kfunc;
 
 	if (!insn->imm) {
 		verbose(env, "invalid kernel function call not eliminated in verifier pass\n");
 		return -EINVAL;
 	}
 
+	*cnt = 0;
+
+	if (bpf_dev_bound_kfunc_id(insn->imm)) {
+		xdp_kfunc = bpf_dev_bound_resolve_kfunc(env->prog, insn->imm);
+		if (xdp_kfunc) {
+			insn->imm = BPF_CALL_IMM(xdp_kfunc);
+			return 0;
+		}
+
+		/* fallback to default kfunc when not supported by netdev */
+	}
+
 	/* insn->imm has the btf func_id. Replace it with
 	 * an address (relative to __bpf_call_base).
 	 */
@@ -15788,7 +15807,6 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 		return -EFAULT;
 	}
 
-	*cnt = 0;
 	insn->imm = desc->imm;
 	if (insn->off)
 		return 0;
@@ -16795,6 +16813,11 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
 	if (tgt_prog) {
 		struct bpf_prog_aux *aux = tgt_prog->aux;
 
+		if (bpf_prog_is_dev_bound(tgt_prog->aux)) {
+			bpf_log(log, "Replacing device-bound programs not supported\n");
+			return -EINVAL;
+		}
+
 		for (i = 0; i < aux->func_info_cnt; i++)
 			if (aux->func_info[i].type_id == btf_id) {
 				subprog = i;